Flywheels are used to store energy in the form of rotational energy. Suitable coupling means can be used to store electric energy in the form of rotational energy in these energy storage devices and, as needed, it can be converted back into electric energy and supplied to a consumer. For the most part, such flywheel energy storage devices have a hollow cylinder as the rotor which stores a certain amount of energy as a function of its rotational speed and mass. The storage capacity of such an energy storage device is limited by its maximum rotational speed. The rotor is usually connected via suitable connection means to a bearing shaft that holds the rotor. The bearing shaft is rotatably mounted in appropriate bearings. The bearing and drive elements are preferably situated on the rotational axis of the rotor. Here, the connection means have the task of connecting and affixing the outer flywheel element (cylinder) to the idle axle (shaft) and of transferring the torsional moment from the drive shaft to the flywheel element and vice versa. The formula for calculating the energy value of a rotary element shows that the rotating element with a high energy value should preferably he configured for a high speed rather than for a high mass. Therefore, nowadays, high-capacity energy storage, devices generally no longer use rotors made of steel, even though steel has a high strength.
Regenerative sources of energy are used nowadays, particularly because of their better environment friendliness as compared to conventional power generating systems. Since, as a rule, these regenerative sources of energy do not supply their energy continuously, there is a great demand for energy storage devices. Therefore, it would be desirable if the energy value of such a flywheel energy storage device could be farther increased while nevertheless lowering the costs for their production.